The invention relates to apparatus for use in a developer station where charge images formed in a charge image carrier passed through the developer station are linked in accordance with magnetic brush principles with a developer mix of toner and carrier particles. Typically, non-mechanical printing or copying machines function according to electrophotographic or xerographic principles, wherein electrostatic latent images of characters to be printed are generated on a charge image carrier, such as a photoconductive drum, and subsequently inked with a black powder known as toner in a developing station. The toner images are subsequently transferred to sheet paper on which they are fixed. The developing station typically includes at least one developer unit generally referred to in the art as a magnetic brush developer. The magnetic brush developer, as a rule, contains a magnetic drum mounted for rotation so as to continually bring developer mix, consisting of iron carrier particles and toner particles, into contact with the electrostatic images recorded on the charge image carrier. The change images are inked by adherence of toner particles to the charge images due to electrostatic forces. The magnetic drum conventionally comprises a rotating hollow cylinder with a stationary magnet arrangment mounted within. One known developer station assembly which functions in accordance with magnetic brush principles is disclosed in U.S. Pat. No. 3,882,821.
In the case of rapid data printers or copiers, the charge images are developed at high speeds. For this purpose, the developer mix is continuously transported past the charge image carrier by the magnetic drum, also known as the developing roller. The direction of rotation and the speed of the developing roller are selected to be such that the charge image carrier containing the latent charge images is correspondingly brushed with developer mix particles as the charge images are conducted through the developing station. As the printing speed increases, the rotational speed of the developing roller must be correspondingly increased, which leads to particle dust generation within the developer station and thus undesirable background inking on the charge image carrier.
Background inking may be prevented when lower relative speeds prevail between the charge image carrier and the developing roller. However, in such an arrangement, the quality of inking of the charge images would deteriorate. A further possibility for avoiding background inking would be to increase the diameter of the developing roller; however, this has the disadvantage that the developing roller would become too large for conventional spatial handling in a developer station.
An object of the present invention is to provide a developer station with apparatus such that, even in the case of highspeed printers or copiers, charge images on the charge image carrier can be effectively inked with high resolution and no inking contamination of the background areas on the charge image carrier.